European patent application EP 1 723 461 relates to a bimorph mirror presenting two ceramic layers having electrodes and spaced apart by a central core.
Such a mirror is assembled in the form of a laminated structure having two so-called “skin” layers, at least one of which is used as a mirror, with the two ceramic layers and the central core being sandwiched between the two skin layers.
Implementing a laminated structure is relatively complicated and difficult.
The laminated structure concept used for bimorph mirrors also limits the dimensions of such mirrors to the dimensions of ceramic elements and to multiples thereof, and the quality with which the mirror is polished is limited by the presence of the laminated structure.
Solutions known in the prior art have always been based on assembling ceramic elements on a face that is parallel to the working optical face.
Under all circumstances, the ceramics are adhesively bonded to a face that is parallel to the optical face, thereby leading to a structure that is laminated in the direction perpendicular to the optical face.
That also applies to document EP 1 835 302 in which the ceramics are adhesively bonded to the face that is opposite from the optical face.
When the ceramic bars are bimorphs, i.e. when the bars comprise two pieces of ceramic stuck back to back, stability is limited by a bimetal type effect when the temperature of the assembly changes.
Furthermore, if the deformable mirror is of dimensions greater than the dimensions of the ceramic elements (which happens very often because of the limited dimensions of commercially-available ceramics), the manufacturer needs to place a plurality of pieces of ceramic end-to-end in order to obtain the necessary dimensions, and in document EP 1 835 302, those junctions between pieces of ceramic are located on the non-optical rear face of the mirror and that discontinuity becomes manifest when the ceramics are put under stress in order to change the curvature of the mirror.